Alight-emitting diode (referred to as “LED” in the following) is known as a light-emitting element including a semiconductor multilayer film. In particular, when a LED for emitting blue light such as a GaN LED is combined with a phosphor that emits green light or red light by excitation of the blue light, the LED can be applied to a light-emitting device for emitting white light.
FIG. 13 is a cross-sectional view of a conventional light-emitting device that emits white light. As shown in FIG. 13, a light-emitting device 100 includes the following: a main substrate 101; a sub-mount substrate 102 mounted on the main substrate 101; a blue LED 104 mounted on a conductor pattern 103 that is provided on the sub-mount substrate 102; and a phosphor layer 105 formed on the sub-mount substrate 102 to cover the blue LED 104. The phosphor layer 105 includes a phosphor that absorbs blue light emitted from the blue LED 104 and emits fluorescence. As such a phosphor, e.g., a yellow phosphor for emitting yellow light, a green phosphor for emitting green light, or a red phosphor for emitting red light is dispersed. In particular, if the green phosphor and the red phosphor are used together, the color rendering of a luminescent color can be improved.
In the light-emitting device 100, however, when the green phosphor and the red phosphor are used together, the red phosphor is excited by not only the blue light emitted from the blue LED 104, but also the green light emitted from the green phosphor. Therefore, part of the green light emitted from the green phosphor may be quenched. To solve this problem, JP 2004-179644 A discloses a light-emitting device in which a green phosphor layer including a green phosphor is formed on a red phosphor layer including a red phosphor.
FIG. 14 is a cross-sectional view of the light-emitting device that has been proposed in 2004-179644 A. As shown in FIG. 14, a light-emitting device 200 includes a blue LED 202 that is mounted in a hollow 201a of a lead frame 201. Moreover, a red phosphor layer 203a covering the blue LED 202 and a green phosphor layer 203b formed on the red phosphor layer 203a are provided in the hollow 201a. The members except at the ends of the lead frame 201 are sealed with a sealing resin layer 204. With this configuration, the green light emitted from the green phosphor layer 203b to the sealing resin layer 204 (i.e., the green light traveling toward the light extraction side) is not absorbed by the red phosphor layer 203a. Accordingly, the configuration can solve at least the problem of quenching of the green component of light produced.
However, in the light-emitting device 200 of JP 2004-179644 A, the blue light emitted from the blue LED 202 or the red light emitted from the red phosphor layer 203a may be refracted or reflected when the light passes through the boundary between the red phosphor layer 203a and the green phosphor layer 203b. Thus, the blue and red components of light produced by the light-emitting device 200 may be reduced, resulting in low luminescence intensity.